1. Field of the Invention
The present invention relates to a silver halide photosensitive material having a dyed hydrophilic colloid layer. More particularly, it relates to a silver halide photosensitive material having a hydrophilic colloid layer containing a photochemically inert dye which absorbs light in the infrared region, and is readily discolored during the photographic processing.
2. Description of the Prior Art
In the field of silver halide photosensitive material, it is a common practice to color a photographic emulsion layer or other layers so that they absorb light of specific wavelengths. Where it is necessary to control the spectral energy distribution of light entering a photographic emulsion layer, a colored layer is included at the position farther from the support than the photographic emulsion layer. Such colored layer is called a filter layer. In the case of such a photosensitive material having a plurality of Photographic emulsion layers, as in the multi-layer color photosensitive material, the filter layer may be interposed between emulsion layers.
When light passes through a photographic emulsion layer or after light has passed through a photographic emulsion layer, light is sometines scattered. The scattered light is reflected by the interface between the emulsion layer and the support or by the surface of the photosensitive material opposite to the emulsion layer and enters the photographic emulsion layer again to cause a halo round the image, i.e. halation. In order to prevent halation, a colored layer was included between the photographic emulsion layer and the support or on the surface of the support opposite to the photographic emulsion layer. This colored layer is called antihalation layer. In the case of multi-layer color photosensitive material, an antihalation layer may be interposed between every adjacent two layers.
The coloring of photographic layers was practiced to prevent the lowering of image sharpness due to light scattering in the photographic emulsion layer (the scattering effect is called irradiation).
The layers to be colored are usually made of a hydrophilic colloidal dispersion. Therefore, in many cases they can be colored with a water-soluble dye. The dye should meet the following conditions.
(1) It should have an adequate spectral absorption according to intended uses.
(2) It should be photochemically inert. In other words, it should not afford chemically adverse effects (e.g., decrease of sensitivity, fading of latent image, and fogging) on the performance of the silver halide photographic emulsion layer.
(3) It should be discolored or dissolved and removed during the photographic processing, and should not leave a color harmful on the processed photosensitive material.
Many conventional dyes which absorb visible light or ultraviolet light are known to meet these conditions. They are suitable for the improvement of image on the conventional photosensitive material sensitized for wavelengths shorter than 700 nm. Typical examples in general use are triarylmethane dyes and oxonol dyes.
Recently, there is a demand for the development of a dye for halation prevention and irradiation prevention which absorbs light in the infrared region. Such a dye is useful for a recording material sensitized to near infrared wavelengths, like a photosensitive material to record the output of near infrared laser.
Such a photosensitive material is exposed by scanning an original. An exposure on the silver halide photosensitive material is performed according to the image signals obtained by scanning. Thus a negative image or positive image corresponding to the original is formed. The recording by scanning method employs as a preferred light source a semiconductor laser. It is small, cheap and capable of easy modulation and it has a longer life than He-Ne laser or argon laser. In addition, since it emits in the infrared region, it allows the use of a bright safelight if the photosensitive material is sensitive to infrared. A bright safelight improves the working environment.
So far, there have been no adequate dyes which have an absorption band in the infrared region and meets the above-mentioned conditions (1) to (3), and consequently there have been few photosensitive materials which have a high sensitivity in the infrared region and is free from halation and irradiation. Under this situation, the semiconductor laser was not fully utilized in spite of its outstanding properties as mentioned above.
Japanese Patent Application (OPI) No. 100116/1085 discloses that an indoaniline dye can be used for the absorption of infrared. However, it had a disadvantage in practical use that it only absorbed infrared rays of short wavelengths. There is disclosed a polymethine cyanine dye in Japanese Patent Application (OPI) No. 64841/1984. Also, there is disclosed a tricarbocyanine dye in British Pat. No. 434,875, U.S. Pat. No. 2,895,955, and Japanese Patent Application (OPI) No. 191032/1984. These dyes have an absorption band in the infrared region but they have a disadvantage of not being photochemically inert.